The invention relates to a process and apparatus for controlling the movement of an injection mold and a handling device.
Injection molding machines and similar apparatuses for molding molded parts from plastic or from other materials are frequently operated in connection with a handling device, robot, manipulator or the like. The handling device or the like has a gripping tool, which can be extended in between the mold halves of the opened mold and withdrawn again, in order to remove the molded part from the mold. The opening and closing movements of the mold and the extending and withdrawing movements of the gripping tool must be carefully coordinated with one another in order that collisions and damage are reliably avoided even in cases of malfunctioning, but on the other hand no unnecessary time losses occur.
"Patent Abstracts of Japan", Volume 11, No. 315, M 631, discloses a control system for the gripping tool of an injection molding machine, in which the position of the movable injection mold is continuously sensed and used as a manipulated variable in a control loop controlling the position of the gripping tool. In an additional control loop, which controls the speed of the gripping tool, the positional deviations of the gripping tool and the reference speed of the movable mold serve as manipulated variables. This control apparatus is elaborate, since it is dependent on a constant position and speed sensing of the movable mold and a speed-controlled drive for the gripping tool. JP-A-62-273816 (Patent Abstracts of Japan, volume 12, No. 152, M 695) discloses an injection molding machine of which the gripping tool carries out a lifting and extending movement perpendicularly to the mold-opening movement and subsequently carries out a co-movement with the opening mold half. The lifting and extending movement commence simultaneously in time with the commencement of the opening of the mold, the co-traveling movement is controlled in dependence on the opening speed of the mold. This control apparatus is also complicated and elaborate, since it requires a gripping tool which can move in three spatial directions and a speed-controllable drive for the co-traveling movement of the gripping tool. If it were wished to apply the principle of these known control systems also to the withdrawing movement of the gripping tool and the closing movement of the mold, even more complicated means would be required for the constant speed control of the closing drive of the injection mold.
It is known to avoid collisions between tools moved at essentially constant, and mutually independent speed, such as for example molding tool and gripping tool, by arranging in each case in the travel of the molding tool and the gripping tool a position transmitter which generates a release signal when the tool concerned has, in its opening or withdrawing movement, reached a position at which the extending or closing movement of the other tool can be safely commenced and completed at a predetermined speed. The position at which the release signal is generated need not be the end position, for example of the opening stroke of the molding tool, but it must be ensured that, when generating the release signal, the molding tool has already covered part of its opening travel and has reached such a position that even if the molding tool jams in this position owing to a malfunction, the gripper can complete its extending movement, triggered by the release signal, without risk of damage. Analogously, the gripping tool emits a release signal for closing the molding tool when it withdraws from the region of the molding tool. This signaling point must also be set in such a way that, in the event of slow travel or a standstill of the gripping tool, damage during closing of the molding tool is ruled out in this position.
By virtue of these safety measures, the movement of the one tool can always be released position-dependently only when the other tool has already covered a considerable part of its movement stroke. Added to this is that both the generation of the release signal and the movement triggered by this in each case takes place with an unavoidable delay, which is caused by the response times of the position sensors, the switching times of the switching elements responding to the position signals and the operating times of the electric, hydraulic or pneumatic final control elements to be driven. These add up to produce considerable time losses, which are at the expense of the cycle rate of the injection molding machine or the like.
The invention is based on the object of designing a process and an apparatus of the specified type in such a way that the movement operations can be carried out with lower non-productive times and in a more favorable time overlap, without thereby increasing the risk of damage in the case of malfunction.
The object of the invention is achieved by providing a process for controlling the relative movement of a molding tool and a gripping tool of a molding machine. The molding tool is movable between a closed position for molding a material and a fully open position. The gripping tool is used to remove a molded workpiece for the molding tool, and is movable between an extended position in which a portion of the gripping tool is within the molding tool when the molding tool is not closed, and a withdrawn position. The process comprises the steps of determining the speed of movement of one of the molding tool and the gripping tool at an intermediate position, determining whether the speed of the one of the molding tool and the gripping tool falls within a predetermined reference range, and, if the speed falls within the reference range, generating a release signal for movement of the other of the molding tool and the gripping tool, and controlling the movement of the other of the molding tool and the gripping tool based upon the release signal.
Another aspect of the invention is a molding apparatus having a molding tool and a gripping tool. The molding tool moves between a closed position for molding the material and a fully open position. The gripping tool is used to remove a molded workpiece from the molding tool. The gripping tool moves between an extended position in which a portion of the gripping tool is within the molding tool when the molding tool is not closed, and a withdrawn position. the apparatus also includes signal generation means for generating a signal indicative of the position of one of the molding tool and gripping tool as a release signal for movement of the other of the molding tool and gripping tool. Furthermore, the apparatus includes control means for controlling the position of the other of the molding tool and the gripping tool. The signal generation means has speed measurement means including means for determining the movement speed of one of the molding tool and the gripping tool at an intermediate position before generating the release signal, and evaluation means to generate the release signal only if the movement speed falls within a predetermined reference range.
According to the invention, not only the position but in addition the speed of the moved tool is used as a criterion for generating the release signal for the other tool. The release signal is generated only if, on passing through the signaling position, the moved tool has a speed corresponding to proper operation. At too low--or possibly even too high--speed, operation is malfunctioned, and the generation of the release signal for the other tool does not occur. This makes it possible to generate the release signal at an earlier point in time of the movement stroke of the tool than was previously possible, in particular already at a position in which the tool has not yet completely cleared the path of movement of the other tool. Establishing that the tool has passed through this position at the proper speed offers adequate certainty that the tool will also properly cover the remaining part of its movement stroke and, as a result, clear the path of movement of the other tool in good time.
In a further refinement of the invention, a repeated or continuous monitoring of the positions and speeds of the two tools can also take place, and it can be established by computational extrapolation whether the two movements will proceed without collision. If there is the risk of collision, the computer can control a corresponding influence on one or both movements, ie. termination, braking or acceleration.